Despite the tremendous interest, an understanding of the onset of crack formation and propagation in nanocomposites is still very incomplete. This is due to a lack of a) characterization techniques to capture the mechanics at sub-100 nm level, and b) accurate models for the estimation of failure-modes. Current models based on linear fracture mechanics fail to capture sub-nanometer crack-tip formation or describe the nanoscale fracture toughness mechanism. Recently, molecular dynamics simulations have helped to illuminate the influence of nanoscale crack length and local void formation on a fracture. However, the accuracy of these simulations relies on refinement of the model parameters from specially designed experiments. With this motivation, the present experiments are designed to illustrate the toughening mechanism of MoS2 reinforced epoxy composites. A systematic processing technique was developed to ensure proper dispersion of the nanocomposites up to 2.0 wt% of MoS2 in a DGEBA epoxy polymer matrix. The detailed characterization using in-situ FT-IR, DSC, and DMA provide insights into the bulk polymer network. AFM-IR enabled visualization of local chemical heterogeneity and interphase formation based on the solvent choice (NMP, acetonitrile) and surface functionality of MoS2. Nanothermal analysis showed localized thermal transition temperatures which are consistent to the Tg values obtained for bulk samples using conventional DSC measurement. High-resolution TEM, SEM, and AFM, as well as nano-X-ray computed tomography, lead to an understanding of the 3D dispersion of these nanosheets. Experiments associated with nanoscale visualization of fracture in the composites are conducted using in-situ tensile testing stages placed within SEM. These experiments indicate cracks propagate along the weak interphase region supporting evidence of variation in the chemical network structure obtained from AFM-IR. These experiments may provide an in-depth understanding of the influence of interphase chemistry, thickness, morphology, and dispersion of nanoparticles on fracture toughness and will be indispensable in guiding the refinement of multi-scale models.

MoS2 dispersed epoxy nanocomposite: Influence of solvent and surface chemistry to local chemical network formation and its influence on nanoscale toughening mechanism

256th National Meeting (2018)

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